DO-OVER! Lawyer Darius Wadia (above) is trying to have evidence against Kasien Adderley dismissed due to errors allegedly made by Mariem Megalla, Photo: Steven Hirsch

(Ellis Kaplan)

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She’s one lucky “lab rat.”

NYPD laboratory technician Mariem Megalla made more than 100 mistakes in 50 of her most recent drug-evidence tests, including what appear to be clear examples of records fraud, according to shocking internal police memos, but she has continued to collect her $69,000 salary and remains criminally uncharged.

Most of the documented screw-ups appear to be of little consequence to the outcome of drug cases, simply amounting to galling sloppiness. Decimal points are misplaced; drug names and item numbers are switched; three bags are listed as one bag; a vial crashes to the floor; data sheets go missing from files.

But police memos obtained by The Post from as recently as last month reveal even more substantial errors as an 18-month investigation by cops and the Queens DA unspools and Megalla continues at full salary in a civilian, nonlab job.

“There should be no inaccuracy at a lab. I mean, people’s lives and freedom are at stake,” complains Manhattan lawyer Darius Wadia, who is representing a Harlem man accused of selling crack cocaine.

In that case, more than 200 milligrams of the drugs Megalla tested have gone missing.

“More than a quarter of the sample disappeared, as if two of the eight crack rocks they charged him [with dealing] have vanished,” Wadia said.

Manhattan Supreme Court Justice Ruth Pickholtz said on Friday that she would rule today on whether to dismiss the evidence in the case against Wadia’s client, Kasien Adderley, 27.

* Some 30 heroin and marijuana samples Megalla said she tested but, in fact, did not.

In the worst example, Megalla wrote she tested all 31 bags of pot from a ’07 bust in Queens, but only tested 13. She also only tested one of eight bags from a Nov. ’08 seizure in the Bronx, according to the internal memos. Fortunately for prosecutors, Megalla guessed right each time, retesting showed.

* Some 15 instances of drug-weight disparities, including two Bronx cases where approximately a gram of coke remains unaccounted for and a 2008 Brooklyn case where Megalla was two grams off in weighing a sample that proved to not be a controlled substance.

“We cannot find any reasonable scientific explanation for the loss of the 912 milligrams,” Thomas Hickey, manager of the police laboratory’s controlled substance analysis section, wrote prosecutors in October regarding an especially grievous case of missing cocaine from one of those Bronx cases.

* Samples of heroin, alprazolam, cocaine, PCP, THC and oxycodone were missed by Megalla entirely as she tested bulk seizures of multiple drugs.

She failed to find the PCP and THC dust on a scale seized by the city-wide Special Narcotics prosecutor, and in one 2009 Staten Island case, she missed a hydrocodeinone pill mingled in a stash of oxycodone pills.

* Drugs were misidentified by name in paperwork. Megalla mislabeled the dust on two drug sifters in a Brooklyn case as cocaine when it was heroin; in another case, she said a sample contained cocaine, heroin and morphine when it contained only cocaine.

For at least six of the 60 defendants mentioned in the memos, Megalla’s accuracy will never be known. Those cases involve drug dust on baggies, envelopes, a straw, even a dealer’s calculator that was entirely consumed by Megalla’s testing, with no residue remaining to be retested.

That includes residual evidence — purportedly of hydrocodone and Zolpidem — from the ongoing murder case of Gigi Jordan, the psychotic millionairess charged with giving her autistic, 8-year-old son a fatal overdose of prescription drugs.

It is unclear if any of the alleged mistakes have resulted in the dismissal of charges.

“While accused of taking shortcuts, I’m not aware of any errors being uncovered beyond the shortcuts themselves, which were not acceptable,” police spokesman Paul Browne said.

She was suspended for 30 days in May, 2010 when the improprieties first surfaced, but has been back on the payroll as required by state civil service law, Browne said.

Megalla’s lawyer, Benjamin Lieberman, insisted, “She never did anything [criminally] wrong. That’s evidenced by the DA never bringing back any charges.”